Evaluation of Longitudinal Desired Dynamics for Dynamic-Inversion Controlled Generic Reentry Vehicles

Abstract

Dynamic inversion is a control synthesis technique in which the inherent dynamics of a dynamical system are canceled out and replaced by desired dynamics, selected by the designer. The output of such an inner-loop controller is the control input, which produces the desired closed-loop response. The desired dynamics essentially form a loopshaping compensator that affects the closed-loop response of the entire system. This paper attempts to quantify the effect of different forms of desired dynamics on the closed-loop performance and robustness of a dynamicinversion ight controller for reentry vehicles. Proportional, proportional-integral, ying-quality,and ride-quality forms of desired dynamics are evaluated using time-domain speci cations, robustness requirements on singular values, quadratic cost, and a passenger ride comfort index. Longitudinal controllers are synthesized for a generic X-38 type crew return vehicle, using a set of linear models at subsonic, transonic, and hypersonic ight conditions. For the candidate forms of desired dynamics and inversion controller structures evaluated here, results indicate that the form used impacts closed-loop performance and robustness and more so for some inversion controller structures more than others. The ride-quality dynamics used with a two-loop angle-of-attack inversion controller provide the best overall system performance, in terms of both time-domain and frequency-domain speci cations, and the evaluation criteria. Jennifer Georgie of Victoria, Texas, earned the B.S. and M.S. degrees in aerospace engineering from Texas A&M University in 1999 and 2001, respectively. She is a recipient of the Distinguished Student Award for Outstanding Academic Achievement from the College of Engineering. From 1996 to 1998 she served three coop tours at the NASA Dryden Flight Research Center, working in the X-31 Flight Controls Group and on the Russian High Speed Civil Transport program in the Aerodynamics Group. For her efforts she was awarded the NASA Dryden Stephen B. Davis Outstanding CoOp Award and the NASA Dryden Spotlight Award twice. From 1999 to 2001 she was a graduate research assistant at Texas A&M, where she worked on ight testing a vision-based automatic landing system and on dynamic inversion controllers for reentry vehicles as a graduate summer intern with the NASA Johnson Space Center. Since June 2001, she has been with Lockheed Martin Aeronautics Company, Fort Worth, Texas, where she is a ight control engineer in the F-16 Block 60 Control Law Design and Analysis group. She is a Member of AIAA.

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Minimum Acceleration Guidance Law for Spaceplane in Ascent Phase via Exact Linearization

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